UC Davis

The intestinal interface allows the host to incorporate and respond to signals from the environment. One way the intestinal contents communicate with the host is through the aryl hydrocarbon receptor (AHR). Highly expressed in the intestinal epithelium and the underlying lamina propria immune cells, the AHR is a cytosolic transcription factor that alters cellular function in a location and cell-dependent manner. Given the evidence that the intestinal environment is dysregulated in type 1 diabetes (T1D), an autoimmunity disorder in which the pancreatic beta cells are attacked, this dissertation examines how modulating AHR signaling in intestinal immune cells may alter diabetes development using the nonobese diabetic (NOD) mouse model of T1D. Chapter 1 is a literature review of AHR signaling in macrophages. The chapter covers what is currently understood about AHR signaling in different contexts, including macrophage differentiation, polarization, function, and immune-mediated diseases. Chapter 2 examines how AHR modulates the gut microbiome during type 1 diabetes development and the role of intestinal CD4+ T cells. Flow cytometric analysis of intestinal CD4+ T cells and 16s microbial data were analyzed from of AHR WT and KO NOD mice at three different time points. Additionally, we utilized specific pathogen-free (SPF) and germ-free (GF) mice to understand the impact of the microbiome on the intestinal CD4+ T cells and diabetes incidence. To investigate how the intestinal T cells interact with the microbiome, we utilized Transkingdom network analysis.

Chapter 3 focuses on the mechanisms occurring upstream of CD4+ T cells in AHR KO NOD mice. Specifically, this chapter identifies intestinal macrophages as a critical target of AhR signaling in the small intestine, utilizing flow cytometry and single-cell RNA sequencing. We then performed experiments using an AHR ligand-enriched diet to demonstrate that macrophages are regulated in an AHR-dependent manner. We provide bioinformatic and functional evidence that suggests these cells interact with intestinal CD4+ T cells in AHR KO NOD mice. Lastly, we used bulk RNA sequencing of intestinal and pancreatic CD45+ cells to perform causal inference analysis to predict how AHR signaling impacts inter-organ communication. Chapter 4 examines the role of AHR signaling in vitro using bone marrow-derived macrophages. Additionally, immunotoxicity of per-and-poly-fluoroalkyl substances (PFAS), ubiquitous environmental pollutants which have been associated with autoimmunity development, is assessed in vitro. By exposing macrophages derived from NOD and B6 mice to PFAS, we model the impact of PFAS exposure in individuals genetically susceptible to T1D. Collectively, the chapters demonstrate that intestinal immune cells are altered by AHR signaling and modulation through AHR signaling may represent a novel mechanism in which the environment influences diabetes development. Additionally, the PFAS study demonstrates that cytokine production is affected by exposure and therefore may alter the host immune response.